Dead Valves?

Quick question for the tube heads on the forum, how do you tell if a valve is dead/malfunctioning? The reason I ask is that having completed my DIY valve phono stage, the PSU is functioning fine but the amplifier stage is as dead as the proverbial dodo . I've checked over the circuit and schematics and everything is in the right place and soldered in fine which leads me to the conclusion that the valves may well be at fault, even though the heaters light up and glow nicely. They're all old RCA/Tung Sol/Raytheon/Slyvania valves that my father salvaged many years ago so it may well be that they have died or developed faults. So apart from sitting there and swapping them in and out to find those that do work are there any other ways to test a valve to see if it's dead? Any suggestions/comments are appreciated.

Cheers,
BL21DE3

 

I'd get a multimeter out first and check all of the voltages.

The only way to test a valve is to test it with a valve tester!! Not easy if you don't have one or know someone who has.

 

Well unfortunately I don't have access to or know anyone with a valve tester so I reckon I'll have to go for the multimeter option. themadhippy suggested in my other thread that it's probably something common to both channels, so short of having made an identical fault in the circuit that leaves either the B+ supply line or the valves. My money is on the valves due to their vintage nature. So I'll try and work my way backwards through the circuit from the output and see if I can find the fault by examining the voltages.

 

All fixed! Not the valves at all, instead it was human error. I'd got two of the resistors in the circuit junctioned wrongly. Thankfully my father spotted it for me this evening. I feel like a proper idiot now.

 

Yeah, I've never made a mistake like that

 

nor me,never got the wiring to the valve bases back to front either

 

Was it a complicated circuit? How long did it take to build? Any pics?

And perhaps more importantly - what does it sound like?


Steve

 

Inidentally - if people ever need valves testing - find an amateur radio forum and ask there. Most amateur radio operators are very friendly - and if they don't have the required valve testing gear, chances are they'll know someone who does.


Steve

 

Steve, see my other thread entitled DIY Phono Stage WIP for some pics of the circuit and the cases I made. It's not a very complicated circuit to follow or put together, especially if you go for the PCB option (but I didn't ), the awkward bits were sourcing some of the components, had to order them from the US in the end (and it worked out approx 50% cheaper than the UK prices even with shipping!). As for how it sounds, I've only had time to test that everything powered up and I got audio signals as I'm still in the process of finishing the cases. But I'm looking forward to getting it up and running.